Methods and apparatus for wireless power delivery and remote sensing using self-capacitances

ABSTRACT

A self-capacitance based remote power delivery device includes a power source, an energy harvesting device, and a substrate. The power source and the energy harvesting device are configured to be capacitively coupled to a self-capacitive body. The substrate is configured to be capacitively coupled to a portion of the self-capacitive body in contact with the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. patent application Ser. No.16/789,007 filed Feb. 12, 2020, which claims priority to U.S.Provisional Patent Application No. 62/804,470 filed Feb. 12, 2019, theentire disclosures of which are hereby incorporated by reference intheir entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with government support under DE027098 awardedby the National Institutes of Health. The government has certain rightsin the invention.

FIELD

The present disclosure generally relates to a wireless power transfersystem.

BACKGROUND

Electronic devices, including hand-held, implantable, and wearableelectronic devices require an energy source in order to function.Supplying power to such devices is an important issue, particularly withimplantable and wearable electronic devices. Many such devices currentlyrely on batteries for power, but batteries may have a relatively lowmechanical stability.

Some electronic devices rely on wireless energy delivery (also referredto as wireless power transfer or WPT) for power. Known WPT techniquesinclude radio-frequency (RF) based, optical-based, bio-cell-based, andultrasound-based wireless energy harvesting. In at least some knownRF-based systems, most of the energy from the energy source is radiatedto the air, there may be interference with external RF devices, and theantenna size may need to be relatively large to utilize lowerfrequencies. Known optical-based systems often use high optical power(e.g., 100 s mW), do not work in the dark, and require properorientation to light to deliver sufficient power. Ultrasound-basedsystems may suffer from decay in signal that increases exponentiallywith distance and frequency, require a transducer in contact with themedium to deliver power inside the medium, and may interfere with nearbyultrasound devices.

Thus, there is a need for improved wireless power transfer systems thatovercome at least some of the above issues with known WPT systems.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

SUMMARY

One aspect of this disclosure is a self-capacitance based remote powerdelivery device. The device includes a power source, an energyharvesting device, and a substrate. The power source and the energyharvesting device are configured to be capacitively coupled to aself-capacitive body. The substrate is configured to be capacitivelycoupled to a portion of the self-capacitive body in contact with thesubstrate.

Another aspect is a self-capacitance based method of remotely deliveringpower. The method includes coupling a power source and an energyharvesting device to a self-capacitive body, capacitively coupling asubstrate to a portion of the self-capacitive body in contact with thesubstrate, and operating the power source to deliver power to the energyharvesting device via the self-capacitive body.

Another aspect of the disclosure is a self-capacitance basedbiotelemetry system. The system includes a power source and substrateincluding an insulating layer and a conductive layer. The conductivelayer is coupled to a power source, and the substrate is configured tobe capacitively coupled to a portion of a self-capacitive body incontact with the substrate. The system also includes a transmitterantenna, a receiver antenna, and a biotelemetry interface devicecapacitively coupled to the self-capacitive body. The biotelemetryinterface device includes a an antenna and an-power oscillator coupledto the antenna and configured to switch an impedance of the antenna.

Various refinements exist of the features noted in relation to theabove-mentioned aspects. Further features may also be incorporated inthe above-mentioned aspects as well. These refinements and additionalfeatures may exist individually or in any combination. For instance,various features discussed below in relation to any of the illustratedembodiments may be incorporated into any of the above-described aspects,alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an illustration of self-capacitance serving as a return pathfor displacement currents emanating from a power-source through theexternal ground back to the source using an electrically isolatedsphere.

FIG. 1B is an illustration of a conventional wireless power-deliverytechnique relying on the mutual coupling between the source and receivertransducers.

FIG. 2A is a diagram of a system for wireless power transfer based onself-capacitance.

FIG. 2B is a diagram of a system for wireless power transfer based onnear and far field radio frequency coupling.

FIG. 2C is a diagram of a system for wireless power transfer based onultrasonic/acoustic coupling.

FIG. 3A is a graph of estimated power transfer efficiencies for thesystem in FIG. 2A when the frequency is 10 MHZ, form factor a_(r) is 10mm, and source resistance R_(s) is 5Ω.

FIG. 3B is a graph of estimated power transfer efficiencies for thesystem in FIG. 2A when the frequency is 10 MHZ, delivery distance d is0.1 m, and R_(s) is 5Ω.

FIG. 3C is a graph of estimated power transfer efficiencies for thesystem in FIG. 2A when the d is 0.1 m, a_(r) is 10 mm, and R_(s) is 5Ω.

FIG. 3D is a graph of estimated power transfer efficiencies for thesystem in FIG. 2A when the frequency is 10 MHZ, a_(r) is 10 mm, and d is0.1 m.

FIG. 3E is a graph of estimated received power P_(r) for the system inFIG. 2A when the frequency is 10 MHZ, a_(r) is 10 mm, and R_(s) is 5Ω.

FIG. 3F is a graph of estimated P_(r) for the system in FIG. 2A when thefrequency is 10 MHZ, d is 0.1 m, and R_(s) is 5Ω.

FIG. 3G is a graph of estimated P_(r) for the system in FIG. 2A when thed is 0.1 m, a_(r) is 10 mm, and R_(s) is 5Ω.

FIG. 3H is a graph of estimated P_(r) for the system in FIG. 2A when thefrequency is 10 MHZ, a_(r) is 10 mm, and d is 0.1 m.

FIG. 4 is a graph comparing power transfer efficiency and received powerP_(r) for different wireless power transfer methods when the receivertransducer dimension is a_(r)=10 mm, f=5 MHz and R_(s)=5Ω.

FIG. 5 is a graph comparing power transfer efficiency and received powerPr for different wireless power transfer methods when the transmissiondistance n is d=0.1 m, f=5 MHz and R_(s)=5Ω.

FIG. 6A is an experimental setup for self-capacitance based wirelesspower transfer using a mouse cadaver.

FIG. 6B is an approximation of self-capacitance for the setup in FIG.6A.

FIG. 6C is a lumped parameter equivalent circuit for the setup in FIG.6A.

FIG. 7A is an experimental setup for self-capacitance based wirelesspower transfer using a mouse cadaver.

FIG. 7B is a measured Smith-chart demonstrating that the substrate inFIG. 7A is predominately capacitive.

FIG. 7C is a graph of the measured voltage at the output of theharvester in FIG. 7A with an input frequency of 10 MHz.

FIG. 7D is a graph of the broad-band response of the setup in FIG. 7Afor a load R_(L) of 1 MΩ.

FIG. 8A is a diagram of an experimental hybrid telemetry setup.

FIG. 8B is a schematic of a battery-based backscattering interface usedas a control in the setup of FIG. 8A.

FIG. 8C is a schematic of a sensing/telemetry interface powered byself-capacitance based wireless power transfer in the setup of FIG. 8A.

FIG. 9A is an experimental setup using a cadaver mouse housed in adiagnostic cage retrofitted with backscattering RF antennas.

FIG. 9B is a picture of the wireless diagnostic cage of FIG. 9A.

FIG. 9C is a schematic of the capacitive coupling setup for the cage ofFIG. 9(b).

FIG. 10A is a photograph showing implantation of a temperature sensor ina cadaver mouse.

FIG. 10B is a battery-powered control prototype for implanting as inFIG. 10A.

FIG. 10C is a self-capacitance based wireless power transfer poweredprototype for implanting as in FIG. 10A.

FIG. 11A is a graph of the spectrum of the backscattered signal receivedat R_(x), when centered around the 915 MHz RF carrier for the prototypein FIG. 10C when implanted in the mouse cadaver as in FIG. 10A.

FIG. 11B is a graph of the change in the modulation frequency as afunction of the temperature, measured using the SC-based implant of FIG.10C.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Example systems and methods for wireless power transfer (WPT) based onself-capacitance (SC-based WPT) are described herein. The SC-based WPTsystems and techniques may be used to provide power to implanted devicesand sensors, such as temperature sensors, neural sensors, oral cavitysensors, heart monitors, and the like. The systems and techniques mayalso be used to power wearable devices, such as smart watches,activity/fitness/performance monitors, smart shoes, smart glasses,insulin pumps, and the like.

The methods and systems are sometime described below with respect tomice and mouse cadavers. It should be understood that the systems andmethods may be applied to humans (and on a human scale) as well.

Self-capacitance is an intrinsic property of any electrically isolatedbody which arises because there always exists fringe electrostaticfields between the body and a theoretical but omni-present,infinitely-large ground plane. In practice, self-capacitances manifestthemselves as parasitic elements that either serve as a nuisance duringsystem design or could be exploited for sensing applications. However,self-capacitances can also serve as a return path for displacementcurrents emanating from a power-source through the external ground backto the source, as illustrated in FIG. 1A using an electrically isolatedsphere.

Since the path traversed by the displacement currents could be long,this attribute has been exploited for designing communication links inwireless body-area-network (WBAN). Conventional wireless power-deliverytechniques rely on the mutual coupling between the source and receivertransducers, as illustrated in FIG. 1B, and therefore the systempower-transfer efficiency (PTE) is determined by the cross-sectionalarea, the relative alignment and the distance between the transducers.As shown in FIG. 1B, the return path for the source transducer current(Is) is separated from the return path of the load transducer current(IL), as a result, the source dissipates a fixed amount of power andonly a fraction of the source power gets coupled to the load. In thecase of self-capacitance, the return path for the source current onlyexists through the load and through the parasitic elements, which maylead to a high power-transfer efficiency (PTE). Also, becauseself-capacitances scale linearly with dimensions, the maximum receivedpower also scales linearly with the receiver form-factor. This is incomparison to inductive WPT approach, where PTE scales as a cube of thesource/receiver coil dimensions. For ultrasound-based and otherfar-field WPT approaches, the transfer-efficiency scales as the squareof the transducer dimensions. Specifically, for power-budgets less than10 μW, SC-based WPT offers significant advantages compared to other WPTmethods, in terms of powering distances, transducer form-factor andsystem scalability. Additionally, the SC-based approach is robust totransducer alignment artifacts, which presents a significant challengefor other WPT modalities.

Aspects of the disclosure include a self-capacitance based simple andtractable wireless power-delivery method that can be used for systemoptimization and comparison with other WPT methods. Compared topreviously reported methods, the self-capacitance based approach isanalytic and can be applied to complex geometries and substrates. Alsodisclosed is a hybrid telemetry system based on RF back-scattering thatis energized using self-capacitance based wireless power transfer.

Self-Capacitance Based Power-Transfer Method

A self-capacitance power delivery method is described below. Beforepresenting a more general SC-based WPT method that could be applied tocomplex geometries and substrates, a simple combined-parameter methodthat can be used for optimization and for comparison with other WPTtechniques is presented. The method, as shown in FIG. 2A-2C, uses ahomogeneous sphere of diameter d as a transmission substrate or as awave-guide. In each of these cases, the objective is to transfer powerfrom the source connected at one end of the substrate, to the loadresistance RL connected to the other end of the substrate. Thepower-transfer efficiency (PTE) η that has been used for comparison isdefined according to Eqn. 1:

$\begin{matrix}{\eta = \frac{P_{r}}{P_{s}}} & (1)\end{matrix}$

where Pr is the power dissipated at the resistor RL and Ps is powerdissipated at the source.

In the SC-based WPT method, as shown in FIG. 2A, the self-capacitance ofthe substrate is Cb. The coupling capacitance Cc and the resistance Rsrepresent the interface between the power-source to the load RL. Asshown in FIG. 2A, the respective displacement currents flow-back to thepower source through Cb and through the self-capacitance of the load,represented by a sphere of radius ar. If d>>ar, then theself-capacitance of the load Cs can be approximated as shown in Eqn. 2:

$\begin{matrix}{C_{s} = {{4\;\pi} \in {{a_{r}{\sum\limits_{n = 1}^{\infty}\frac{\sinh\left( {\ln\left( {D + \sqrt{\left( {D^{2} - 1} \right)}} \right)} \right)}{\sinh\left( {n\mspace{14mu}{\ln\left( {D + \sqrt{\left( {D^{2} - 1} \right)}} \right)}} \right)}}} \geq {4\;\pi}} \in a_{r}}} & (2)\end{matrix}$

In Eqn. 2, the E is the dielectric constant of the medium andD=(d/a_(r)) where d is the distance between the load and the substrate.Irrespective of the magnitude of the ratio D, the self-capacitance Cscan be lower-bounded, as shown in Eqn. 1, which represents theworst-case self-capacitance. This simpler, worst-case expression is usedto estimate the minimum power that can be delivered to RL.

Applying standard circuit analysis technique to FIG. 2A, the efficiencyof power transfer is shown in Eqn. 3, as derived as shown in Example 1:

$\begin{matrix}{\eta = \frac{1}{1 + {R_{L}{R_{s}\left( {{4\;\pi^{2}} \in_{0}{fd}} \right)}^{2}} + {\frac{R_{s}}{R_{L}}\left( {1 + \frac{d}{2\; a_{r}}} \right)^{2}}}} & (3)\end{matrix}$

FIGS. 3A-3H plot the efficiency (η) and received power (Pr) fordifferent values of RL, Rs, ar, d and f. Results show that η and Pr varymonotonically with respect to Rs, ar, d and f, except for the loadresistance RL. Thus, the expression in Eqn. 3 can be maximized withrespect to RL, in which case the maximum power transfer efficiency ηmaxis obtained as shown in Eqn. 4:

$\begin{matrix}{\eta_{\max} = \frac{1}{{1 + {8\;\pi^{2}}} \in_{0}{{fR}_{s}\left( {a_{r} + d + \frac{d^{2}}{2\; a_{r}}} \right)}}} & (4)\end{matrix}$

The maximum efficiency is achieved for the condition

$R_{L} = \frac{1}{C_{s}\omega}$

and the corresponding power dissipated by the load R_(L) is given byEqn. 5:

$\begin{matrix}{P_{r,\max} = {\frac{C_{s}\omega\; V_{s}^{2}}{2\left( \frac{C_{c} + C_{b}}{C_{c}} \right)^{2}} = \frac{{4\;\pi^{2}} \in_{0}{{fa}_{r}V_{s}^{2}}}{\left( {1 + \frac{{2\;\pi} \in_{0}d}{C_{c}}} \right)^{2}}}} & (5)\end{matrix}$

In Eqn. 5, it is assumed Rs=0 since Pr is monotonic with respect to Rs.

The expressions in Eqns. 4 and 5 are used for comparing the PTE of theSC-based method with other WPT approaches, as summarized in FIGS. 4 and5. In the case of RF-based WPT, as shown in FIG. 2B, the energy isdelivered over the air, rather than through the substrate, where as inthe case of inductive and ultrasound based WPT the power is deliveredthrough the medium, as shown in FIGS. 2B and 2C. The expressions for thepower transfer efficiency η for each of the WPT approaches (Ind:inductive, RF: far-field radiofrequency and US: ultrasound) are given byEqn. 6:

$\begin{matrix}{\eta = \left\{ \begin{matrix}{Q_{r}Q_{t}\eta_{r}\eta_{t}\frac{a_{r}^{3}a_{t}^{3}\pi^{2}}{\left( {d^{2} + a_{t}^{2}} \right)^{3}}} & {Ind} \\{\frac{G_{r}G_{t}}{4}\left( \frac{2\; a_{r}}{\pi\; d} \right)^{2}} & {RF} \\{\frac{a_{r}^{2}}{a_{t}^{2}}e^{{- 2}\;\alpha\; f^{\beta}d}} & {{US},}\end{matrix} \right.} & (6)\end{matrix}$

where

Q_(t)=Quality factor of the transmitter coil.

Q_(r)=Quality factor of the receiver coil.

η_(t)=efficiency of the transmitter coil.

η_(r)=efficiency of the receiver coil.

a_(t)=radius of the transmitter.

a_(r)=radius of the receiver.

d=Distance between transmitter and receiver.

G_(t)=Gain of transmitter antenna.

G_(r)=Gain of receiver antenna.

f=frequency of US wave (Hz).

α=Attenuation Parameter (neper/mMHz^(−β)).

β=Attenuation Coefficient.

Representative parameter values are summarized in Table I below. FIG. 4shows that as the transmission distance increases, the SC-based WPTdemonstrates a superior PTE compared to the other WPT techniques. Inthis comparison, the diameter of the receiver transducer (coil orantenna size) was chosen to be a_(r)=10 mm. In FIG. 5, the PTEs fordifferent WPT approaches as the transducer form-factor is varied whilekeeping the delivery distance constant at d=0.1 m are compared. Theresults show SC-based WPT demonstrates a superior PTE compared to otherapproaches. Note that for the other WPT approaches, the transferfrequency needs to be adjusted to ensure ideal impedance matchingbetween the antenna/transducer to the substrate. SC-based WPT isbroad-band in nature (as verified in experimental results shown below),and therefore does not require any frequency adjustment when thetransducer size or alignment changes.

TABLE I PARAMETERS USED FOR COMPARING DIFFERENT WPT METHODS [17].Property Description Value C_(c) Source coupling capacitance 10 pF αAttenuation parameter 0.086 (neper/mMHz^(−β)) β Attenuation Coefficient1.5 G_(t) Gain of Tx antenna 7.5 dB G_(r) Gain of Rx antenna 7.5 dB

Using the self-capacitance based method, the framework may extend tosubstrates with arbitrary shapes and comprised of heterogeneousmaterials. The method is illustrated here using a mouse model as asubstrate and is shown in FIG. 6A. The method can be extended to otheranimal models as well. As shown in FIG. 6A, the power source iscapacitively coupled (through capacitance C_(c)) to the tail of themouse and the energy harvester is connected to one of the fore-limbs.The harvester in this example comprises of a rectifying diode bridgewhich drives the load resistance R_(L) and the reference terminal isconnected to a floating-electrode.

The self-capacitance of the mouse body is estimated by first segmentingdifferent regions of the substrate and approximating each region using asimple shape, for example a sphere or a cylinder, as shown in FIG. 6B.The closed-form expressions for self-capacitances in each of thesesimple 3-dimensional shapes are well documented and can be estimated asa function of their respective dimensions. For example, theself-capacitance of a cylindrical shape is estimated asC_(cylinder)=2πϵh/n (r₂/r₁) where h is the length of cylinder, r₁ and r₂are the inner and outer radii of the cylinder and ϵ is the permittivityof the substrate. Similarly, for a spherical shape (modeling the head),the self-capacitance is given by C_(spherical)=4πϵr₁. With respect tothe energy-harvester, each of the self-capacitances (C_(b1), C_(b2),C_(b3), C_(b4), C_(b5) and C_(b6)) can be considered to be in parallelto each other (independent path for displacement currents to flow-backto the source). If the capacitive cross-coupling between these differentshapes is ignored, all of the elements could be combined together into asingle capacitance C_(b) to form the equivalent circuit shown in FIG.6C. FIG. 6C also shows a cross-coupling capacitance between thefloating-electrode and the body self-capacitance. In some instances, ifthe size of the floating-electrode is small, the coupling capacitancemay be ignored. The equivalent circuit in FIG. 6C also shows a combinedresistance R_(s) that models the resistivity between the couplingelectrode and the harvester. In its exact form, R_(s) and C_(b) wouldinclude distributed elements, but as shown in experimental results,R_(s)≈0, leading to the combined equivalent circuit shown in FIG. 6C.

Characterization of SC-Based Power Delivery

In a set of experiments, a mouse cadaver model was used to characterizean SC-based power delivery. The experimental setup is shown in FIG. 7Awhere the cadaver is kept electrically insulated from environmentalfactors to ensure a capacitive coupling between the body and return path(external ground in this case). The material and methods for storing andreviving the cadaver in this experiment is described in Example 2.First, an impedance analyzer (Omics Bode 100 vector network analyzer)was used to measure the equivalent impedance between the source and theharvester. The resulting Smith-chart corresponding to the frequency of10 MHz is shown in FIG. 7B which shows that the substrate impedance ispredominantly capacitive. This is true even when a resistive load isconnected to the energy-harvester, as the body self-capacitance is muchlarger than the self-capacitance of the floating-electrode. Next, amodulating energy source (an earth-grounded Tektronix DG4102 functiongenerator) is capacitively coupled to the tail of the cadaver. The powersource is programmed to generate a sinusoidal wave at a potential of 20V_(pk-pk) and at variable frequencies. The harvester comprised of asingle-stage diode bridge shown in FIG. 7A constructed using twoSchottky diodes. The output of the diode bridge was measured using abattery-powered voltmeter with no direct conductive path to ground.Also, connected to the diode-bridge is a load resistor whose magnitudecould be varied. Note that the other end of the diode bridge forms thefloating-electrode providing a return path for the load-current to thesource.

FIG. 7C shows the measured voltage across different the load-resistanceas the resistance value is varied. For this experiment the sourcevoltage was programmed to 20 V_(pk-pk) with an operating frequency of 10MHz. Based on the plot in FIG. 7C, it can be estimated the deliveredpower to be approximately 45 μW. As described in Eqn. 5, the deliveredpower may be increased by increasing the size of the couplingcapacitance or by increasing the size of the floating-electrode'sself-capacitance. In another experiment, the voltage across the loadR_(L)=1 MΩ was measured for different operating frequencies. The resultis shown in FIG. 7D, which shows a broadband response within thefrequency range of 1-15 MHz. This result can be understood using theequivalent circuit model shown in FIG. 6C. The input coupling capacitorC_(c) blocks low-frequencies whereas the coupling capacitor C_(p)bypasses high-frequencies to the load R_(L). Also, at higher frequenciesthe substrate itself acts as an antenna and hence manifests as aradiation resistance in parallel with the load resistance R_(L).

SC-based WPT can be exploited for designing power-efficient animal cagesfor long-term and ambulatory monitoring applications. Previous designsof smart animal cages have used inductive coils embedded inside theflooring of the cage. Since the SC-based WPT operates by capacitivelycoupling an energy source through the body of the animal, the insulatedbase of the cage can be directly used as the coupling capacitor. This isshown in FIG. 8A, where power is coupled through different body segmentsas an animal is moving around in the cage. Note that the seriesresistance of a thick conductive underlay R_(s) could be very small (onthe order of 2.65*10⁻⁸ Ω·m), which implies that the PTE according toEqn. 4 may be close to 100%. Size limitations on the floating-electrodeself-capacitance may limit power delivery to any ex-vivo part of theanimal body to power levels on the order of microwatts. This limitationmay be overcome by using a hybrid telemetry approach as shown in FIG.8(a-c). The power harvested from the SC-based WPT approach is used tomodulate the impedance of an RF antenna on the device S, in FIG. 8A.This modulation is then received as a backscattered RF signal emitted bythe transmitter antenna T_(x) and received by the receiver antennaR_(x).

This approach has previously been effectively used for backscatteringWi-Fi signals and for biotelemetry applications. Two examples of thebiotelemetry interface are shown in FIGS. 8B and 8C. In both designs, alow-power oscillator T is used to switch the impedance of the antenna B.The frequency of the oscillator and hence the modulation frequency ofthe antenna is determined by a resistor R_(L) whose value changesaccording to the sensor signal being sensed. Thus, the sensor signal iseffectively backscattered on the signal received by the receiver R_(x).FIG. 8B represents a battery powered variant of the telemetry interfaceand has been used for control experiments, whereas FIG. 8C representsthe variant that is powered using SC-based WPT approach.

An apparatus used for the operation of a hybrid telemetry system isshown in FIG. 9A. A mouse cadaver is used to emulate the animal in adiagnostic cage. The bottom overlay of the cage, as shown in FIG. 9B isdesigned using an Aluminum sheet (6Ω) that is sandwiched between twoPlexiglas insulators. The sheet is then connected to one of the outputsof a power source, as shown in FIG. 9C. Two 915 MHz ultra-high-frequency(UHF) antennas, Tx and Rx were used for backscattering. Both theantennas were controlled by a Software Defined Radio (Ettus ResearchUSRP N210) and were programed to transmit a carrier frequency and toreceive the backscattered signal.

The mouse cadaver is implanted with a device that can monitor variationsin temperature at target locations in vivo and then backscattering themeasurements to the receiver R_(x). The surgical set up is shown in FIG.10A and the surgical protocol is described in Example 2. The two typesof implants (powered using a battery and powered using SC-based WPT) areshown in FIGS. 10B and 10C. The temperature sensor was implemented usinga (NCP15WM474E03RC) thermistor whose temperature sensitivity is given by(5.1 kOhm/° C.). The tip of the thermistor was surgically implanted at adepth of 3 cm. The output of the thermistor was used to bias a TS3006timer that implemented the backscatter according to the schematicdescribed in FIG. 8. The backscatter was designed to operate on asingle-supply voltage range between 1.55 V and 5.25 V with typicalsupply currents remaining below 2.4 μA. FIG. 11A shows the spectrum ofthe backscattered signal received at R_(x), when centered around the 915MHz RF carrier. To locally heat the tissue, another piece of wire wasinserted in proximity to the area where the tip of the thermistor waslocated. Heat was applied to the other end of the wire externally whichwould lead to change in resistance at the output of the thermistor. Thisin turn would change the modulation frequency (labeled as A) in thereceived spectrum. FIG. 11B plots the change in the modulation frequencyas a function of the temperature, measured using the SC-based implant.The result shows a monotonic response in the frequency shift withrespect to temperature with less than 1% variance between the threetrials. Thus, by measuring the frequency shift one could accuratelyinfer the magnitude of the in vivo temperature. The average measuredresponse is compared against the average response measured from thebattery-powered implant. The result shows that the error between the twooutputs Δf is negligible.

Table II shows the comparison of an exemplary self-capacitance based WPTwith the most recent topologies in terms of efficiency, form factor andthe distance of power delivery. From the table, it can be seen that thedisclosed SC-based WPT has advantages compared with the efficiency, formfactor and comparable power delivery distance for wearable electronics.

TABLE II REF Modality Foam Factor Distance Efficiency MisalignmentSensitivity Method [37] 2018 Ind u_(r) = 40 mm × h = 115 mm  70 mm   70%Yes ex-vivo [38] 2017 Ind a_(r) = 50 mm 120 mm   72% Yes ex-vivo [39]2018 Ind a_(r) = 33 mm  6 mm  58.6% Yes ex-vivo [40] 2018 Ind 20 mm × 50mm N/A 15.92% Yes ex-vivo [41] 2016 US N/A  7 mm   25% Yes in-vivo [42]2015 Rad  a_(r) = 2 mm  40 mm  0.04% Yes in-vivo [43] 2017 Cap a_(r) =60 mm  7 mm   66% Yes in-vivo [44] 2018 Cap a_(r) = 83 mm  15 mm  2.6%Yes in-vivo This work Cap a_(r) = 10 mm  70 mm   90% No ex-vivo

A wireless power transfer method based on the intrinsicself-capacitances of substrates is disclosed. Compared to other WPTapproaches, SC-based WPT demonstrates higher PTE, for example when thetarget power-budgets are in the order of microwatts. Also disclosed is atractable, combined-parameter method for SC-based WPT that could be usedfor system optimization and comparison. This method has been validatedusing experimental results which demonstrate a broad-band response (1-15MHz) for harvestable power budgets of 20-200 μW. Furthermore, SC-basedWPT can demonstrate PTE (η>90%) for distances greater than 10 cm whichmakes it attractive for large-scale power delivery. The diagnostic cage,as shown in FIG. 9B could be scaled to larger dimensions, housingmultiple ambulatory animals. Also, the power source is capacitivelyconnected to the body, which will obviate the initiation of anyelectrochemical reactions at the electrode surface. Using thecombined-parameter method, the maximum harvestable power for SC-basedWPT scales linearly with the dimensions of the receiver transducer, andas a result, the size of the wearable or implant antenna may be reducedsignificantly. Note that the FDA limits on power dissipation forSC-based WPT are estimated to be 2.5 mW/mm² which is significantlyhigher than the microwatts power-budget described herein.

Thus the disclosed approach could be scaled to larger animals like humansubjects through the use of wearables and under-the-skin implantables.There are several approaches to boost the power that can be delivered tothe load using the disclosed SC-based WPT. Increasing the couplingcapacitance C_(c) in the equivalent model in FIG. 6C is one possibleapproach. However, this approach may require modifying the dielectricproperty of the substrate or the body. The power may be boosted byincreasing the open-load voltage of the source as described by Eqn. 5.Note that this is viable option as long as the voltage is within thelimits of the dielectric breakdown of the material forming C_(c).Another option to boost the delivered power is to increase the size ofthe self-capacitance of the energy harvester C_(s), described by theEqn. 5. Note, however, that the received power scales linearly with thedimensions of the receiver transducer/antenna, and as a result may bebest suited with a certain range of form-factors.

Self-capacitance C_(s) is a parasitic element that will change based onthe distribution of the fringe electric-field. However, given a specificform-factor a_(r) and the shape of the floating-electrode, one couldlower-bound the size of C_(s) using a close-form expression as shown inEqn. 2 for a spherical geometry. This therefore signifies the worst-caseC_(s) for which R_(L) and minimum delivered power could be estimated.However, to further enhance the delivered power, a post-deploymentcalibration and adjustment of R_(L) according to the actualself-capacitance value may be performed. Also self-capacitance may leadto an electrostatic charge build up due to floating-electrodes. However,note that the WPT method using 1 MHz-15 MHz AC and the DC potentials atthe source and the remote device are decoupled from each other. So, thechange in DC potential will not affect the WPT. In terms of safety, theself-capacitance of the floating-electrode is in the order pico-faradsor less. Therefore, the charge build-up at the device may be relativelysmall. Safety related to electrostatic charge buildup on the bodyself-capacitance is similar to ESD safety. The method disclosed hereinmay apply to an ambulatory animal or a human body. The robustness of theself-capacitance based WPT is due in part to the fact that theefficiency degrades only linearly with distance (as shown in FIG. 4), sothe approach is robust to ambulatory artifacts. A worst-caseconfiguration would be when only the tail of the mouse is in contactwith the floor and experimental setup in FIG. 7 verified the WPT forthat configuration. Note that in all other ambulatory states, there willalways be additional capacitive coupling path to the body (unless theanimal is in the air). Also, any energy fluctuations due to motionartifacts may be filtered out by the energy regulation unit on theharvester.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present disclosure. It should be appreciated by those of skill inthe art that the techniques disclosed in the examples that followrepresent approaches the inventors have found function well in thepractice of the present disclosure, and thus can be considered toconstitute examples of modes for its practice. However, those of skillin the art should, in light of the present disclosure, appreciate thatmany changes can be made in the specific embodiments that are disclosedand still obtain a like or similar result without departing from thespirit and scope of the present disclosure.

Example 1: Derivation of PTE and Received Power for SC-Based WPT

For the circuit shown in FIG. 2 (a) denote:

$\begin{matrix}{{Z_{s} = \frac{1}{j\;\omega\; C_{s}}}{Z_{b} = \frac{1}{j\;\omega\; C_{b}}}{Z_{c} = \frac{1}{j\;\omega\; C_{c}}}{{Then},\begin{matrix}{V_{o} = {{Vs}\;\frac{R_{L}}{R_{L} + Z_{s}}\frac{\left( {R_{L} + Z_{s}} \right) \parallel Z_{b}}{\left( {R_{L} + Z_{s}} \right) \parallel {Z_{b} + \left( {Z_{c} + R_{s}} \right)}}}} \\{= \frac{R_{L}Z_{b}V_{s}}{{\left( {Z_{c} + R_{s}} \right)\left( {R_{L} + Z_{b} + Z_{s}} \right)} + {Z_{b}\left( {R_{L} + Z_{s}} \right)}}}\end{matrix}}} & (7)\end{matrix}$

which leads to

$\begin{matrix}{P_{r} = {\frac{V_{o}^{2}}{R_{L}} = {\frac{R_{L}V_{s}^{2}}{{{{\left( {\frac{C_{b}}{C_{c}} + {j\; R_{s}C_{b}\omega}} \right)\left( {R_{L} - {j\;\frac{C_{s} + C_{b}}{C_{s}C_{b}\omega}}} \right)} + \left( {R_{L} - {j\;\frac{1}{C_{s}\omega}}} \right)}}^{2}} = \frac{R_{L}V_{s}^{2}}{\left( {{R_{L}\left( {1 + \frac{C_{b}}{C_{c}}} \right)} + {R_{s}\left( {1 + \frac{C_{b}}{C_{c}}} \right)}} \right)^{2} + \left( {{R_{L}R_{s}C_{b}\omega} - \frac{C_{c} + C_{b} + C_{s}}{C_{c}C_{s}\omega}} \right)^{2}}}}} & (8) \\{Z_{in} = {\left( {Z_{c} + R_{s}} \right) + \frac{Z_{b}\left( {R_{L} + Z_{s}} \right)}{\left( {R_{L} + Z_{b} + Z_{s}} \right)}}} & (9) \\{P_{s} = {\frac{V_{s}^{2}}{Z_{in}} = {\frac{V_{s}^{2}}{{\left( {Z_{c} + R_{s}} \right) + \frac{Z_{b}\left( {R_{L} + Z_{s}} \right)}{\left( {R_{L} + Z_{b} + Z_{s}} \right)}}} = \frac{V_{s}^{2}\left\lbrack {R_{L} + {R_{L}^{2}{R_{s}\left( {C_{b}\omega} \right)}^{2}} + {R_{s}\left( {1 + \frac{C_{b}}{C_{c}}} \right)}^{2}} \right\rbrack}{\left( {{R_{L}\left( {1 + \frac{C_{b}}{C_{c}}} \right)} + {R_{s}\left( {1 + \frac{C_{b}}{C_{c}}} \right)}} \right)^{2} + \left( {{R_{L}R_{s}C_{b}\omega} - \frac{C_{c} + C_{b} + C_{s}}{C_{c}C_{s}\omega}} \right)^{2}}}}} & (10)\end{matrix}$

The PTE (η) can then be estimated according to equation 1 as

$\begin{matrix}{{\eta = \frac{R_{L}}{R_{L} + {R_{L}^{2}{R_{s}\left( {C_{b}\omega} \right)}^{2}} + {R_{s}\left( {1 + \frac{C_{b}}{C_{s}}} \right)}^{2}}}{\eta = \frac{1}{1 + {R_{L}{R_{s}\left( {{4\;\pi^{2}} \in_{0}{fd}} \right)}^{2}} + {\frac{R_{s}}{R_{L}}\left( {1 + \frac{d}{2\; a_{r}}} \right)^{2}}}}} & (11)\end{matrix}$

The PTE can be maximized with respect to R_(L) by setting:

${\frac{\partial\eta}{\partial R_{L}} = 0},{{R_{L} \approx \frac{1}{{8\;\pi^{2}} \in_{0}{fa}_{r}}} = \frac{1}{C_{s}\omega}}$

which leads to

$\begin{matrix}{\eta_{\max} = \frac{1}{{1 + {8\;\pi^{2}}} \in_{0}{{fR}_{s}\left( {a_{r} + d + \frac{d^{2}}{2\; a_{r}}} \right)}}} & (12)\end{matrix}$

Example 2: Cadaver Material and Methods

As a proof of concept, experiments have been conducted on the mousecadaver. Mouse cadavers were selected because they are easy to workwith, and the cadavers accurately model the electrical characteristicsof a live animal, provided they have been stored and revived properly.Since a live animal and a cadaver will both have capacitive coupling tothe floor of the mouse cage, the WPT mechanism generally operates forboth live animals and cadavers.

In one experiment, a battery-based electronic circuit was surgicallyimplanted subcutaneously within the mouse cadaver. The battery andcircuit were placed subcutaneously along the dorsum of the back. Athermistor was implanted underneath the interscapular adipose tissue.The incision was closed with glue to prevent exposing the implant inorder to perform the measurements. The measured temperature data of themouse tissue was used as a reference for a second experiment in whichthe battery-less wearable electronic circuit that harvests the energythrough the self-capacitance methods described herein was implemented.Three mouse cadavers were used to statistically verify results andcompare with the reference data. There was no direct contact between themouse cadaver and the electric power source, but instead an insulatedwire was wrapped around the mouse tail to form a coupling capacitor.

Definitions and methods described herein are provided to better definethe present disclosure and to guide those of ordinary skill in the artin the practice of the present disclosure. Unless otherwise noted, termsare to be understood according to conventional usage by those ofordinary skill in the relevant art.

In some embodiments, numbers expressing quantities of ingredients,measurements, properties such as molecular weight, reaction conditions,and so forth, used to describe and claim certain embodiments of thepresent disclosure are to be understood as being modified in someinstances by the term “about.” In some embodiments, the term “about” isused to indicate that a value includes the standard deviation of themean for the device or method being employed to determine the value. Insome embodiments, the numerical parameters set forth in the writtendescription and attached claims are approximations that can varydepending upon the desired properties sought to be obtained by aparticular embodiment. In some embodiments, the numerical parametersshould be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof some embodiments of the present disclosure are approximations, thenumerical values set forth in the specific examples are reported asprecisely as practicable. The numerical values presented in someembodiments of the present disclosure may contain certain errorsnecessarily resulting from the standard deviation found in theirrespective testing measurements. The recitation of ranges of valuesherein is merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range. Unlessotherwise indicated herein, each individual value is incorporated intothe specification as if it were individually recited herein.

In some embodiments, the terms “a” and “an” and “the” and similarreferences used in the context of describing a particular embodiment(especially in the context of certain of the following claims) can beconstrued to cover both the singular and the plural, unless specificallynoted otherwise. In some embodiments, the term “or” as used herein,including the claims, is used to mean “and/or” unless explicitlyindicated to refer to alternatives only or the alternatives are mutuallyexclusive.

The terms “comprise,” “have” and “include” are open-ended linking verbs.Any forms or tenses of one or more of these verbs, such as “comprises,”“comprising,” “has,” “having,” “includes” and “including,” are alsoopen-ended. For example, any method that “comprises,” “has” or“includes” one or more steps is not limited to possessing only those oneor more steps and can also cover other unlisted steps. Similarly, anycomposition or device that “comprises,” “has” or “includes” one or morefeatures is not limited to possessing only those one or more featuresand can cover other unlisted features.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.“such as”) provided with respect to certain embodiments herein isintended merely to better illuminate the present disclosure and does notpose a limitation on the scope of the present disclosure otherwiseclaimed. No language in the specification should be construed asindicating any non-claimed element essential to the practice of thepresent disclosure.

Groupings of alternative elements or embodiments of the presentdisclosure disclosed herein are not to be construed as limitations. Eachgroup member can be referred to and claimed individually or in anycombination with other members of the group or other elements foundherein. One or more members of a group can be included in, or deletedfrom, a group for reasons of convenience or patentability. When any suchinclusion or deletion occurs, the specification is herein deemed tocontain the group as modified thus fulfilling the written description ofall Markush groups used in the appended claims.

All publications, patents, patent applications, and other referencescited in this application are incorporated herein by reference in theirentirety for all purposes to the same extent as if each individualpublication, patent, patent application or other reference wasspecifically and individually indicated to be incorporated by referencein its entirety for all purposes. Citation of a reference herein shallnot be construed as an admission that such is prior art to the presentdisclosure.

Having described the present disclosure in detail, it will be apparentthat modifications, variations, and equivalent embodiments are possiblewithout departing the scope of the present disclosure defined in theappended claims. Furthermore, it should be appreciated that all examplesin the present disclosure are provided as non-limiting examples. Asvarious changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing(s) shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A self-capacitance based remote power deliverydevice comprising: a power source electrically configured to becapacitively coupled to a self-capacitive body; an energy harvestingdevice, the energy harvesting device configured to be capacitivelycoupled to the self-capacitive body; and a substrate, wherein thesubstrate is configured to be capacitively coupled to a portion of theself-capacitive body in contact with the substrate.
 2. Theself-capacitance based remote power delivery device of claim 1, whereinthe power source is electrically coupled to the substrate.
 3. Theself-capacitance based remote power delivery device of claim 1, whereinthe energy harvesting device is coupled to the substrate.
 4. Theself-capacitance based remote power delivery device of claim 1, whereinthe substrate is configured to be capacitively coupled to a portion ofthe self-capacitive body in direct contact with the substrate.
 5. Theself-capacitance based remote power delivery device of claim 1, whereinthe substrate is a grounded substrate.
 6. The self-capacitance basedremote power delivery device of claim 1, wherein the power sourcecomprises a modulating power source.
 7. The self-capacitance basedremote power delivery device of claim 1, wherein the energy harvestingdevice comprises a rectifying diode bridge connected to a loadresistance.
 8. A self-capacitance based method of remotely deliveringpower, the method comprising: capacitively coupling a power source andan energy harvesting device to a self-capacitive body; capacitivelycoupling a substrate to a portion of the self-capacitive body in contactwith the substrate; and operating the power source to deliver power tothe energy harvesting device via the self-capacitive body.
 9. Theself-capacitance based method of claim 8, further comprisingcapacitively coupling the power source to the substrate.
 10. Theself-capacitance based method of claim 8, further comprisingcapacitively coupling the energy harvesting device to the substrate. 11.The self-capacitance based method of claim 8, wherein capacitivelycoupling the substrate to a portion of the self-capacitive body incontact with the substrate comprises capacitively coupling the substrateto a portion of the self-capacitive body in direct contact with thesubstrate.
 12. The self-capacitance based method of claim 8, furthercomprising connecting the substrate to ground.
 13. The self-capacitancebased method of claim 8, wherein the power source comprises a modulatingpower source, and operating the power source to deliver power to theenergy harvesting device via the self-capacitive body comprisesoperating the modulating power source at an operating frequency todeliver power to the energy harvesting device via the self-capacitivebody.
 14. The self-capacitance based method of claim 8, wherein theenergy harvesting device comprises a rectifying diode bridge connectedto a load resistance.
 15. A self-capacitance based biotelemetry systemcomprising: a power source; a substrate comprising an insulating layerand a conductive layer, wherein the conductive layer is coupled to thepower source, and the substrate is configured to be capacitively coupledto a portion of a self-capacitive body in contact with the substrate; atransmitter antenna; a receiver antenna; and a biotelemetry interfacedevice capacitively coupled to the self-capacitive body, thebiotelemetry interface device comprising: an antenna, and an oscillatorcoupled to the antenna and configured to switch an impedance of theantenna.
 16. The self-capacitance based biotelemetry system of claim 15,wherein the biotelemetry interface device further comprises: a resistor;a rectifying diode bridge; and a floating electrode coupled to areference terminal.
 17. The self-capacitance based biotelemetry systemof claim 15, wherein the substrate comprises a grounded substrate. 18.The self-capacitance based biotelemetry system of claim 15, wherein theoscillator comprises a low-power oscillator.
 19. The self-capacitancebased biotelemetry system of claim 15, wherein the biotelemetryinterface device's antenna comprises a radio frequency antenna.
 20. Theself-capacitance based biotelemetry system of claim 15, wherein thepower source comprises a modulating power source.